This invention relates in general to electrophotography and more specifically, to an electrophotographic imaging member with an improved charge blocking layer and process for using the imaging member.
In the art of electrophotography an electrophotographic plate comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated area. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
As more advanced, complex, highly sophisticated, electrophotographic copiers, duplicators and printers were developed, greater demands were placed on the photoreceptor to meet stringent requirements for the production of high quality images. For example, the numerous layers found in many modern photoconductive imaging members must be uniform, free of defects, adhere well to to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a drum or belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a hole blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer. This photoreceptor may also comprise additional layers such as an overcoating layer. Although excellent toner images may be obtained with multilayered photoreceptors, it has been found that the numerous layers limit the versatility of the multilayered belt photoreceptor. For example, these drums often comprise a metal substrate having a roughed surface to avoid plywooding effects that can occur with laser exposure systems. It has been found that when the drums are dip coated, the hole blocking layer does not consistently form a thick uniform coating on the roughened surface and often leaves uncovered bares spots at the peaks of the roughened substrate surface. These bares spots directly impact copy print quality because they print out as white spot defects on negatively charged photoreceptors. Also, the hole blocking layer coating tends to spontaneously develop extensive layer cracking after drying at elevated temperature to facilitate curing. Thus, there is a great need for mass production dip coating of high quality long service life photoreceptor drums. Cracks developed in charge blocking layers during cycling were manifested as print-out defects which adversely affected copy quality. Moreover, alteration of materials in the various belt layers such as the hole blocking layer, can adversely affect overall electrical, mechanical and other electrophotographic imaging properties of the photoreceptor such as residual voltage, background, dark decay, adhesion and the like, particularly when cycled thousands of times in environments where conditions such as humidity and temperature can change daily.